board: rockchip: Set SFC1 pin mode on FriendlyElec NanoPi M5

NanoPi M5 uses the M1 pin configuration for its serial flash controller.
Set the pin mode to M1 explicitly to enable SPL loading from SPI flash.

Signed-off-by: Alexey Charkov <alchark@gmail.com>

Author: alchark

arch/arm/dts/rk3576-nanopi-m5-u-boot.dtsi

@@ -15,6 +15,9 @@
 };
 
 &sfc1 {
+	pinctrl-0 = <&fspi1m1_csn0 &fspi1m1_pins>;
+	pinctrl-names = "default";
+
 	flash@0 {
 		bootph-pre-ram;
 		bootph-some-ram;